Diabetes-Induced Cardiomyocyte Passive Stiffening Is Caused by Impaired Insulin-Dependent Titin Modification and Can Be Modulated by Neuregulin-1

Rationale: Increased titin-dependent cardiomyocyte tension is a hallmark of heart failure with preserved ejection fraction (HFpEF) associated with type-2 diabetes mellitus (T2DM). However, the insulin-related signaling pathways that modify titin-based cardiomyocyte tension, thereby contributing to modulation of diastolic function, are largely unknown. Objective: We aimed to determine how impaired insulin signaling affects titin expression and phosphorylation and thus increases passive cardiomyocyte tension, and whether metformin or neuregulin-1 can correct disturbed titin modifications and increased titin-based stiffness. Methods and Results: We used cardiac biopsies from human diabetic (n=23) and non-diabetic patients (n=19), cultured rat cardiomyocytes, left ventricular tissue from ApoE-/- mice with STZ-induced diabetes (n=12-22), and ZSF-1 rats (n=5-6) and analyzed insulin-dependent signaling pathways that modulate titin phosphorylation. Titin-based passive tension was measured using permeabilized cardiomyocytes. In human diabetic hearts, we detected titin hypo-phosphorylation at S4099 and hyper-phosphorylation at S11878, suggesting altered activity of protein kinases; cardiomyocyte passive tension was significantly increased. When applied to cultured cardiomyocytes, insulin and metformin increased titin phosphorylation at S4010, S4099 and S11878 via enhanced ERK1/2 and PKCα activity; neuregulin-1 application enhanced ERK1/2 activity but reduced PKCα activity. In ApoE-/- mice, chronic treatment of STZ-induced diabetes with neuregulin-1 corrected titin phosphorylation via increased PKG and ERK1/2 activity and reduced PKCα activity, which reversed the diabetes-associated changes in titin-based passive tension. Acute application of neuregulin-1 to obese ZSF-1 rats with T2DM reduced end-diastolic pressure. Conclusions: Mechanistically, we found that impaired cGMP-PKG signaling and elevated PKCα activity are key modulators of titin-based cardiomyocyte stiffening in diabetic hearts. We conclude that by restoring normal kinase activities of PKG, ERK1/2 and PKCα, and by reducing cardiomyocyte passive tension, chronic neuregulin-1 application is a promising approach to modulate titin properties in HFpEF associated with T2DM.